A Long Term Evolution (LTE) system supports two duplex modes, namely, Frequency Division Duplex (FDD) and Time Division Duplex (TDD). Compared with FDD, TDD does not need paired frequency spectrum resources, thereby providing more flexible system configurations. Currently, with regard to each frame containing 10 subframes, TDD-LTE can provide 7 different subframe configurations for uplink and downlink distributed asymmetrically. As shown in the following Table 1, these subframe configurations can provide 40%-90% downlink subframes, presenting flexible service adaptability characteristics. In particular, D in Table 1 represents a downlink subframe, U an uplink subframe, and S a special subframe. A special subframe consists of a downlink Orthogonal Frequency Division Multiplexing (OFDM) symbol, a blank protective interval and an uplink OFDM symbol, wherein the downlink OFDM symbol accounts for a large proportion and is used for transmitting control information and data information. Therefore, usually a special subframe is approximated as a downlink subframe.
TABLE 1SwitchingUplink andperioddownlinkof uplinkcon-andSubframe No.figurations downlink012345678905 ms0SUUUDSUUU15 msDSUUDDSUUD25 msDSUUDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUUDDDDDD65 msDSUUUDSUUD
In an existing mobile communication system, all cells of a network will be statically set with the same TDD Uplink/Downlink (UL/DL) configuration to reduce inter-cell interference and management complexity. When a homogeneous network is covered by a macro base station, since a large number of subscribers are served by the macro base station, the statistical rules of the covered area are stable and consistent, thus it is suitable to use the method for statically setting all the cells of the network with the same uplink and downlink subframe configuration. However, with development of wireless communication, low power access points, such as micro base stations, pico base stations, household base stations, and radio remote units etc., are introduced on a large scale. In this case, since fewer subscribers are served by low power access points, and most of them are covered by hot points, dynamic changes of uplink and downlink service amounts of the areas covered by low power access points are remarkable, and obvious difference exists in the uplink and downlink service amounts among different low power access points. Therefore, it is necessary for each cell to dynamically perform TDD UL/DL configuration.
In the case of dynamically configuring TDD UL/DL, different cells will dynamically select suitable subframe configurations based on condition of their service amounts, requiring greater flexibility and adaptability. However, in another aspect, as adjacent cells select different uplink and downlink subframe configurations, cross interference between uplink and downlink subframes among different cells, that is, inter-base station interference and inter-user interference will be introduced. For example, with regard to one TDD subframe, it may be a downlink subframe for Cell 1 and an uplink subframe for Cell 2; the base stations for Cell 1 and Cell 2 may cause inter-base station interference (such as the BS-BS interference shown in FIG. 1), and the user equipment (UE) in Cell 2 and Cell 1 may cause inter-UE interference (such as the UE-UE interference shown in FIG. 1).
In a statically configured TDD network, since the TDD UL/DL configuration for each cell is the same, in the respective downlink subframes, interference to the receiving terminal, that is, the UE comes from the downlink transmission power of the BSs in other cells, and is relatively stable, therefore, a channel quality indicator (CQI) value may be measured and reported within a certain CQI reporting period (the periods for reporting channel quality information in TD-LTE include 1 ms, 5 ms, 10 ms, 20 ms, 40 ms, 80 ms and 160 ms), to assess the channel conditions of all downlink subframes in one frame (the CQI measurement process is as below in the prior arts: in a certain CQI reporting period, one subframe is selected to perform CQI measurement and reports a CQI value within a designated reporting period; a time point for a user to report CQI is configured by high level signaling at the BS side). But in a dynamically configured TDD network, interference of a static downlink subframe in a target cell basically comes from the downlink transmission power of the BSs of other cells, while interference of a dynamic downlink subframe may come from the downlink transmission power of the BSs in other cells or the uplink transmission power of the users in other cells. Therefore, for dynamic TDD configurations, interference conditions of the respective downlink subframes may differ greatly, so the traditional CQI measuring and reporting manner cannot reflect the changes of the interference conditions of the respective downlink subframes in the dynamic TDD configurations, causing reduced system performance.
At present, in case of dynamic TDD UL/DL configurations, there is no effective solution to the problem that an effective CQI measuring and reporting cannot be performed in the prior arts.